Disabled state label, value/placeholder and hint text color are all $gray40.

Hint text

A optional message under an input. It comes in three states: An instruction, a warning, and disabled. A simple line of text with special instruction (e.g. "Required for security purposes", or "Password must be over 8 characters"). See a spec for a hint message.

Errors

For accessibility, it's important to distinguish errors by more than just a change of color. Errors should always be explained using a warning hint message, in addition to the input border color changing to $red50.